Skip to main content

208 Boulder field

ISOM 2017-2
208 Boulder field (ISOM 2017-2)

Geometry: area.


An area which is covered with so many scattered blocks of stone that they cannot be marked individually, is shown with randomly placed and orientated solid triangles with sides of ratio 8:6:5 (inner angles: 92.9, 48.5, 38.6). A boulder field will generally not impact runnability. If the runnability of the boulder field is reduced, symbol 209 (dense boulder field) should be used or the symbol should be combined with a stony ground symbol.

A minimum of two triangles should be used. One triangle may be used if it is combined with other rock symbols (for instance directly below cliff symbols (201, 202), adjacent to boulder symbols (204-206) or combined with stony ground symbols (210-212)).


The maximum distance (centre to centre) between neighbouring triangles: 1.2 mm.

The minimum distance (centre to centre) between neighbouring triangles: 0.75 mm.

Density: 0.8-1.0 symbol / mm2. To be able to show obvious height differences within a boulder field, it is permitted to enlarge some of the triangles to 120%.

Footprint of individual triangle: 12 m x 6 m.

Colour: black.

Correct examples